1. Field of the Invention
The invention generally relates to an image capturing device, in particular, to an image capturing device and an auto-focus method thereof.
2. Description of Related Art
With development in technology, various smart image capturing devices, such as tablet computers, personal digital assistants and smart phones, have become indispensable tools for people nowadays. Camera lenses equipped in high-end smart image capturing devices provide same or better specifications than those of traditional consumer cameras. Some high-end types not only provide specifications such as 10 or more megapixels, large aperture, anti-handshake, and dual lenses, but also provide near-equivalent pixel qualities to those of digital single lens reflex cameras.
In terms of an image capturing device with dual lenses, it may attain a stereo image display by using depth information obtained during image capturing and dynamically adjust a focus region for captured images to provide additional features unavailable in an image capturing device with a single lens. When such dual-lenses image capturing device captures images, it often turns off one of the lenses to become a conventional single-lens image capturing device and performs an auto-focus algorithm according to the clarity of the images captured by the single lens. However, while the single lens is performing auto-focus, the rate for capturing an image per second (i.e. frame per second, fps) in a darker scene would need to be lower due to a longer exposure time and thus cause a slow focus speed.